a. Field of Invention
The invention relates generally to devices and methods for demonstrating aspects of cardiovascular physiology. Particularly, the invention relates to a device and method for demonstrating how elastic major arteries, in conjunction with high downstream resistance and an upstream cardiac outflow valve, smooth out the fluctuations in arterial blood flow. Secondly, the invention demonstrates that the work required to drive flow of a particular magnitude is lessened by the presence of elastic major arteries.
b. Background of the Invention and Description of Related Art
The cardiovascular system is basically a pressure driven transport system, moving its constituents macroscopic distances within an organism, coupled to diffusional transport systems that move constituents microscopic distances. The invention focuses on the convective, macroscopic elements of the cardiovascular system. The fluid, blood, is pressurized in the heart and then moves along a pressure gradient to the tissues throughout the body. Blood pressure and blood flow cycle according the cardiac cycle, diastole to systole. Systole is the contraction phase of the cycle in which blood is pressurized and then ejected. Diastole is the relaxation phase in which the ventricle is filled.
The Elastic Properties of Arteries: Arteries are elastic blood vessels that convey blood away from the heart. Arteries are not rigid like metal pipe. Rather, arteries have elastic properties that allow the size (cross sectional area) of the artery to vary based on blood pressure. At a given location, an artery expands to accept the volume of blood ejected from the heart. As the volume of blood passes downstream, the artery returns to a less expanded state as the pressure decreases in the diastolic phase. The elasticity of arteries allows the arteries to effectively store the contractile energy that the ventricle generates during systole and release it during diastole, maintaining arterial pressure within a more narrow, higher range than would occur if the arteries were rigid. Maintenance of a high arterial pressure throughout the cardiac cycle preserves the pressure gradient driving blood flow, causing a more constant flow rate throughout the cycle, even though the heart ejects blood only intermittently. If arteries were inelastic, blood flow would only occur at systole. Elastic arteries accept pulses of blood volume from the heart and normalize the pulses into a continuous flow. Elastic arteries also reduce the workload on the heart during ejection. The stroke volume is the volume of blood ejected by the heart each beat. By expanding to accommodate a large proportion of the stroke volume during systole, the elastic arteries reduce the immediate flow rate through the high resistance downstream vessels. This reduction in flow rate through the high resistance represents a workload reduction for the heart. As arteries stiffen, the work required to generate the same amount of flow increases.
Arterial elasticity is an important concept in the field of cardiovascular physiology. The flexible nature of tissue in elastic arteries remains vital for proper circulation. Cardiovascular disease is the primary cause of death across the globe. One aspect of cardiovascular disease develops when arteries become damaged and lose their elasticity.
No stand-alone apparatus of the simplicity of the invention is known that performs the function of the invention. However, artwork describing the general concept of the elasticity of blood vessels is typical in general physiology textbooks (e.g., Human Physiology: From cells to systems by Lauralee Sherwood (7th Edition); Brooks/Cole, 2009) and cardiovascular physiology textbooks (e.g., An Introduction to Cardiovascular Physiology, by J. R. Levick (4th Ed.); Oxford University Press, Inc., New York, 2003). Furthermore, more complex and cumbersome models of cardiovascular systems can demonstrate the concept (e.g., J Steketee, Demonstration model of the human circulation. Eur. J. Phys. 2: 150-154, 1981), but not in the simple fashion of the present invention.
An object of the present invention is to provide a simplified device and method for demonstrating the fluid flow physics and the beneficial effects of elastic arteries.